1. Field of the Invention
The present invention relates to a subscriber line control device in an electronic exchange, and more particularly, to a subscriber line control device including hardware and software for controlling Layer 1 according to transmission line regulations in the physical layer of ISDN subscriber lines.
2. Description of the Related Art
This subscriber line control device is connected to subscriber circuits and controls Layer 1 by means of SD/SCN signals. An SD signal is a transmission signal which conducts relay control for maintenance operations by activating the transmission path forming the physical layer of the subscriber lines. On the other hand, the SCN signal is a signal for indicating subscriber circuit fault information and synchronization between the subscriber circuits and the terminal devices.
FIG. 16 is a structural example of a subscriber control system including a subscriber line control device. This is constituted by a subscriber control shelf 1, a line processor (LPR) 2 and a call processor (CPR) 3. Subscriber line control devices 10 are incorporated in the subscriber control shelf 1.
The subscriber control shelf 1 further comprises circuits 12 providing an interface function with the line processor 2 and call processor 3, and a plurality of subscriber cards 11 (card 0xe2x88x92n). The plurality of subscriber cards 11 are connected respectively to ISDN terminal subscribers by means of terminal devices NTE, and accommodate, for example, eight subscriber circuits. In the configuration illustrated in FIG. 16, the subscriber line control devices 10 form a duplex redundancy structure (#0, #1) and are each connected respectively to a plurality of subscriber cards 11.
In the configuration shown in FIG. 16, only the active subscriber line control devices 10 of the system currently in use communicate with the host (line processor 2 and call processor 3). Therefore, the active subscriber line control devices 10 receive control signals for the subscriber lines from the host, and notify the host of subscriber line faults.
Here, in order to control the plurality of subscriber lines, the subscriber line control devices 10 scan the plurality of subscriber cards 11 in succession, detect state changes in all of the subscribers (for example, 224 subscribers), and transmit these changes to the host. Changes in the SCAN (SCN) signal obtained when the subscriber cards 11 are scanned are also detected periodically by the subscriber line control devices 10 for all the subscribers, by means of firmware.
On the other hand, with the progress of rationalization in recent years, there has been a tendency to increase the number of subscriber cards accommodated by a subscriber control shelf 1. In this case, a problem arises in that the processing load on the firmware increases as the number of subscriber lines rises.
In other words, to explain this with reference to the drawings, FIG. 17 shows a structural example previously developed by the present inventors for application to the subscriber line control devices 10 shown in FIG. 16. In FIG. 17, an SD/SCN control section 100 forming a hardware device, receives SCAN signals from the subscriber cards 11. The SCAN signals received by the SD/SCN control section 100 are transmitted to the SCAN memory 101 where SCAN data (0)xe2x88x92(n) for all the subscribers is recorded successively.
Here the contents of the SCAN data include, for example, fault information for the corresponding subscriber line, subscriber circuit-terminal device synchronization bits, and the like.
FIG. 18 is a flowchart of firmware operations relating to FIG. 17. SCAN data for each subscriber is read from the SCAN memory 101 (step S1), and the SCAN data for the corresponding subscriber referred to last (Last-Look) is read from a firmware memory 102 (step S2).
These respective data items are compared by a firmware comparison process 103 (step S3). If the data do not agree, then the contents of the firmware memory 102 are updated (step S4), and for each subscriber number, a notification is sent to the Layer 1 control program on the subscriber line control device indicating that there has been a change in the SCAN signal (step S5). This processing is carried out for each subscriber (step S6).
The Layer 1 control program conducts Layer 1 activation processing and fault processing on the basis of this notification of change in the SCAN signal. Accordingly, with this configuration there has been a problem in that the firmware processing load increases as the number of subscribers rises.
Therefore, it is an object of the present invention to resolve the problem of increased firmware processing load when the number of subscribers rises, by providing a subscriber line control device which enables the firmware processing load to be reduced regardless of increases in the number of subscriber lines.
It is a further object of the present invention to provide, in a duplex redundancy configuration of subscriber line control devices (#0, #1), a subscriber line control device which enables the SCAN signal to be carried over to a new ACT system without leakage, when the system is switched.
In a subscriber line control device connected to a plurality of subscriber circuits, the aforementioned objects of the present invention are achieved by providing, a memory circuit for recording signal data indicating the states of subscriber lines, and hardware for displaying flags denoting changes in the signal data indicating the states of the subscriber lines, as well as firmware for monitoring periodically the flags displayed by the hardware.
In one mode, the present invention is characterized in that in the foregoing, there is provided a comparison circuit for comparing signal data indicating the states of the subscriber lines previously recorded in the memory circuit with received signal data indicating the states of the subscriber lines, and when this comparison circuit detects a disagreement, the memory circuit is updated by writing received signal data indicating the state of a subscriber line into the memory circuit, and the aforementioned flag is set as a flag indicating that the signal data has changed.
In a further mode, in the foregoing, when the firmware refers to a flag and the flag indicates that the signal data has changed, the firmware reads out the corresponding signal data written into the memory.
In yet a further mode, when the comparison circuit has detected a disagreement, if the corresponding flag is one which indicates that the signal data has changed, then neither the process of updating the signal data in the memory circuit, nor that of changing the flag, are implemented.
Moreover, a FIFO memory is provided, and this FIFO memory indicates the location in the memory circuit where the received signal data is to be written, when the comparison circuit detects a disagreement.
Yet further, in the foregoing, the location indicated in the FIFO memory is decremented when the firmware has read the signal data in the memory circuit, and it is incremented when the comparison circuit detects a disagreement.
Using an active and stand-by duplex configuration in a subscriber line control device connected to a plurality of subscriber circuits, the present invention is characterized in that it comprises, as hardware components, memory circuits for recording signal data indicating the states of subscriber lines, for an active system and a stand-by system, respectively, and means for displaying flags denoting changes in this signal data indicating the states of the subscriber lines, as well as firmware for monitoring periodically the flags displayed by the display means, and the active system rewrites and updates the current and stand-by memory circuits, when this flag display means indicates that there has been a change in the signal data indicating the states of the subscriber lines, and the stand-by system periodically rewrites the flags for all subscribers as flags indicating that there has been no change in signal data.
In the foregoing, in one mode, the stand-by system rewrites the memory circuit unconditionally when a flag indicates that there has been a change in signal data.